Chairs of the type typically used in offices and the like are usually configured to allow tilting of the seat and backrest as a unit, or to permit tilting of the backrest relative to the seat. Typically, however, the seat and back are not individually adjustable, and are not individually articulated during tilting. Such chairs therefore sometimes cannot be easily adjusted or customized by the user to accommodate the particular size, shape and/or desired posture of the user.
For example, the seat is typically formed as a relatively rigid, or fixed component, without any articulation between various body-supporting portions of the seat. As such, when a user tilts rearwardly in the chair, the user may tend to slide forward in the seat, even when tilting rearwardly. At the same time, any adjustment of the depth of the seat, measured from the front leading edge to the rear thereof, typically is provided by moving the entirety of the rigid, unitary seat in a fore-aft direction, which can lead to an unsightly gap forming at the rear of the seat and can also form a pinch point at that location. Moreover, such chairs must provide for structure to allow the seat to move relative to the backrest while at the same time bearing the load of the seat and user. Moreover, such chairs typically must employ an extra support member which allows the seat to move thereon, for example, when the seat and/or support member are integrated into the linkage assembly.
In typical tilt chairs, a static angular position of the chair back relative to the seat is typically fixed when the chair is in an unloaded upright position, which may not be particularly well suited for a wide range of users. Moreover, the back is typically formed as a relatively rigid, or fixed component, again without any articulation between various portions of the back. As such, the chair back does not allow the user a full range of motion, precluding for example the ability of the user to stretch or arch their back in a concave contour.
Tilt chairs normally employ compression and/or tension springs, torsion springs and/or torsion bars, or leaf springs to bias the seat and back upwardly and to counterbalance the rearward tilting of the user. The mechanisms used to adjust the load on the spring(s), or the load capability of the spring(s), typically are complicated, and/or require multiple, excessive rotations of a knob or other grippable member to obtain the desired setting. Moreover, the chairs lack any indicia for the user to determine the setting of the return force of the spring before the user sits or applies a load to the backrest.
Moreover, such tilt chairs often do not provide a balanced ride throughout the range of tilting motion of the chair. Specifically, the restoring force or torque of the chair, and in particular the spring, does not match the force or torque applied by the user throughout the tilting range. Although the applied force and restoring force may balance out at a particular tilt position, such balance does not typically occur throughout the tilting/recline range. Moreover, such balance typically cannot be achieved for a variety of users having different weights and body sizes. As such, the user must exert energy and/or apply an external force to maintain the chair in a particular location.